That apartment one in the city would be an absolute dog box and not good for larger groups.
If you want to make noise, Flemington would be the way to go.
Port Melbourne can be a tad 'precious' so would steer clear of this.
Have a couple of podcasts or something to chuck on early in the night whilst you wait for a few people to get there.
personally I'd mix quick(ish) because 18 year olds have the attention span of a goldfish at times.
be prepared to play some super shit music, because that's what the people want.